1. Field of the Invention
The present invention relates generally to motion picture projectors, and more particularly to film transport systems and methods by which film is advanced through a motion picture projector.
2. Description of the Background Art
Motion picture film consists of a succession of still images or frames, which are sequentially projected onto a surface to produce the illusion of motion. A motion film projector is configured to transport each frame from a feed reel or spool to an aperture block, where it is held in stationary register for a period of time required for projection of the associated image. The frame is thereafter transported to a take-up reel or spool. Similarly, a motion film camera is configured to transport each unexposed frame from a first location to the aperture block, where the frame is held in stationary register during exposure of the frame, and thereafter to a second location in the camera.
Large-format motion picture film projectors conventionally employ a rotor-stator rolling loop design to transport film in the desired manner. Projectors of this type have a relatively large rotor adapted with angularly spaced gaps and a curved stator for guiding the film between the rotor and the stator. As the rotor rotates, loops of film are formed in the rotor gaps, and these gaps move the loop one frame length each time a loop passes a set of stationary register pins on the stator. Each film loop develops continuously in a rotator gap by receiving a continuously fed supply of film as the gap travels from a film inlet to an aperture block. Likewise, each loop diminishes in size as it travels from the aperture block to a film outlet. The stator register pins are positioned adjacent to the aperture block to hold sections of the film stationary during projection. Exemplary film transport mechanisms of the foregoing general description are disclosed in U.S. Pat. Nos. 3,494,524 and 3,600,073 to Jones and Shaw, respectively.
The above-described rolling loop design has several disadvantages associated therewith. One limitation of this design is that the projector lamp assembly must be positioned interiorly of the rotor. This requirement presents significant restraints on the size, shape, and configuration of the projector lamp assembly. In addition, the presence of the rotor about the projector lamp assembly may interfere with access thereto.
Another disadvantage associated with the above-described rolling loop design is that the rotor must be mounted very precisely with respect to the stator. Any shaft wobble or other misalignment will cause the rotor to rub against the film, thereby increasing film wear and decreasing the film's lifetime. This condition is particularly undesirable in large-format film projectors, which utilize film prints costing many thousands of dollars.
Moreover, the rotor element of this rolling loop design is expensive to manufacture. In particular, the rotor element must be machined to relatively tight tolerances. These stringent machine tolerances translate directly into higher manufacturing costs for each rotor, thus raising the cost of manufacturing for each rotor-stator projector system.
Another limitation of conventional projectors, including the rotor-stator projector, is that they tend to be difficult, and therefore expensive, to maintain. In particular, when the rotor bearings wear out, a major overhaul of the projector is typically required to replace the bearings. Such an overhaul requires a significant amount of technician time. Perhaps more importantly, the overhaul process requires a considerable amount of "down time" for the projector. Both the technician time and the projector down time can be very expensive.
An additional limitation of the above-described rolling loop projectors is that they are large and heavy. For example, commercial embodiments of this design weigh on the order of 2,500 lbs. In addition to being heavy, these commercial embodiments are typically about five feet wide, five feet long, and almost six feet in height. Indeed, due to the dimensions and weight of these projectors, they require a relatively large area in which to operate and are difficult to transport. Consequently, the size and weight of these projectors is further and significant disadvantage.
Another proposed film transport system is the straight line transport system described in connection with FIGS. 7 and 7A of U.S. Pat. No. 3,494,524 to Jones mentioned above. This system includes a flexible band with gaps formed therein. Loops of film are then positioned within the gaps and advanced onto and off register pins on the aperture block.
This straight line transport system, however, has several disadvantages. For example, this system does not provide ample shuttering of the film while it is in register with the aperture block. Without properly shuttering the film while it is in register with the aperture block, the projected image will contain a relatively high degree of flicker. Additionally, this system is likely to cause significant wear on the film due to the relatively sharp angles through which the film must pass as it rides in the band gaps. Indeed, as shown in FIG. 7A of the Jones patent, the film must bend through sharp angles adjacent to the leading and trailing edges of the band gaps. Passing film through such angles at the high rates of speed common to such projectors would significantly increase the wear on and, thus, decrease the life of the film passing therethrough.
Accordingly, a need exists to provide a motion picture film projector that does not require a rotor-stator configuration. Moreover, a need exists to provide a motion film projector that permits the lamp housing, to be positioned external of the film advancement mechanism. Another need exists to provide a motion picture film projector that has reduced size and weight to facilitate transport and operation of the projector. Additionally, a need exists to provide a motion picture film projector that limits the wear of the film. Further, a need exists to provide a motion film projector that may be maintained relatively easily and inexpensively.